1. Field of the Invention
The present invention generally relates to actuators used for performing mechanical work and, more particularly, to fluidic artificial muscles, artificial muscle actuators, or McKibben artificial muscles.
2. Description of Prior Art
Fluidic artificial muscles (also known as artificial muscle actuators, or McKibben artificial muscles, among other names), are simple mechanical actuators that harness pressurized fluid (air, water, oil, etc.) to generate significant forces and deflections.
Fluidic artificial muscles commonly comprise an inner elastic fluid bladder surrounded by a stiff braided sleeve that is sealed on each end to allow for pressurization, though co-cured bladder-braid, layered helical windings, and straight fibers are also options.
The operating principle of fluidic artificial muscles is as follows. Pressurization will produce force and motion, either contractile or extensile, due to the interaction between the bladder and braided sleeve. The inner elastic, bladder is pressurized with a fluid such as air or oil, causing an inflation and expansion of the bladder. The braided sleeve around the bladder is thereby forced to expand. However, the fixed length of the stiff sleeve fibers generates a contractile or extensile force along the main axis of the actuator, in addition to relative motion between the two end fittings. The direction of force and motion are dependent on the initial angle between the filaments of the braided sleeve. For a contractile actuator, the bladder expansion is radial and for an extensile actuator, the bladder expansion is primarily axial. This force and motion is transferred to an external system via the end fittings.
Fluidic artificial muscle actuators of this type have been known in prior patent publications. A related device was disclosed in April 1957 in U.S. Pat. No. 2,789,580. Many different designs have been disclosed over the years (U.S. Pat. Nos. 2,844,126, 4,733,603, and 4,751,869., but few of these have led to successful commercialization. Some more recent designs, such as those disclosed in (U.S. Pat. Nos. 4,615,260 and 6,349,746), have led to commercial products. Fluidic artificial muscles have attracted interest in the fields of robotics, industrial automation, and recently aerospace engineering (see applicant's co-pending U.S. patent application Ser. No. 11/502,360) because of their simple design, light weight, compliance, and excellent performance in terms of forces and deflections generated.